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Eingeladener Vortrag
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Vibration measurements have many causes and many technical and natural sources. Problems can sometimes be solved by short-term measurements, but in many cases, a long-term measurement is necessary. In long-term measurements of days, weeks, months and even years, it is easy to collect a huge quantity of raw data, but at the end, the post-processing of these data can be exhausting (for example one-year vibration data of a wind energy tower). A software has been developed which con-sists of measuring and evaluation routines where the measuring routines can operate different meas-uring systems and different measuring cards. The main advantage of this software is the fact that the interesting evaluations can be integrated in the measuring process so that the characteristics of the vibration can be extracted without storing all the raw data. Only important time segments are stored, for example train passages. The overall concept of the software and the main evaluation routines will be described in some details. Examples of our measurement experience will illustrate the capabilities of the software. 1) Surveying construction work in nearby sensitive buildings (for example an old wind tunnel), including a stable alarm system and meaningful vibration limits. 2) Prediction of train-induced vibration for a planned building to prevent annoyance and to improve the building design. 3) Modal analysis and long term measurements of several single- or multi-span, concrete or steel bridges 4) Modal and wave analysis of coupled floors in a historical building (“Neues Palais” at Potsdam). 5) Soil properties of various measurement sites (different routines to evaluate the dispersion). Moreover, from many projects, amplitudes, frequencies, and attenuation laws have been collected and analysed for the different sources such as vibratory or impact pile driving and ground compaction, demolition work with different machines, blasting in quarries and in tunnel works, bomb and mine clearing.
Numerical simulators, such as finite element models, have become increasingly capable of predicting the behaviour of structures and components owing to more sophisticated underlying mathematical models and advanced computing power. A common challenge lies, however, in calibrating these models in terms of their unknown/uncertain parameters. When measurements exist, this can be achieved by comparing the model response against measured data. Besides uncertain model parameters, phenomena like damage can give rise to further uncertainties; in particular, quasi-brittle materials, like concrete, experience damage in a heterogeneous manner due to various imperfections, e.g. in geometry and boundary conditions. This hardens an accurate prediction of the damaged behaviour of real structures that comprise such materials.
In this study, which draws from a data-driven approach, we use the force-version of the finite element model updating method (FEMU-F) to incorporate measured displacements into the identification of the damage parameters, in order to cope with heterogeneity. In this method, instead of conducting a forward evaluation of the model and comparing the model response (displacements) against the data, we impose displacements to the model and compare the resulting force residuals with measured reaction forces. To account for uncertainties in the measurement of displacements, we endow this approach with a penalty term, which reflects the discrepancy between measured and imposed displacements, where the latter is assumed as unknown random variables to be identified as well. A Variational Bayesian approach is used as an approximating tool for computing posterior parameters. The underlying damage model considered in this work is a gradient-enhanced damage model.
We first establish the identification procedure through two virtual examples, where synthetic data (displacements) are generated over a certain spatially-dense set of points over the domain. The procedure is then validated on an experimental case-study; namely a 3-point bending experiment with displacement measurements resulting from a digital image correlation (DIC) analysis.
Die Definition und Beschreibung der Einfügedämmung im Normentwurf DIN 45673-4 ist noch nicht richtig. Es wird die Beschreibung aus DIN 45673-3 herangezogen, die für Messungen gilt. Für die drei Rechenverfahren gibt es jeweils eine passende Beschreibung. Mit diesen Vorlagen ist eine vernünftige Definition der Einfügungsdämmung zu finden. Es bedarf einer Abgrenzung gegenüber anderen (falschen) Möglichkeiten. Des Weiteren ist der Anhang 2 erweitert und der Parametersatz im Anhang 1 auf das Wesentliche reduziert worden.
There is no applicable existing standard for the determination of safety characteristics for hybrid mixtures. While developing a new standard in a joint research project in Germany first results from parameter studies led to a standard procedure that can be adopted by laboratories that are already testing dusts in the so called 20L-sphere with as little additional effort as necessary. In fact, one of the main objectives of this research project was to keep modifications and adjustments from the generally accepted dust testing procedures as easy and minimal as possible so as to limit potential deviations from one laboratory to another.
In this first round robin test on hybrid mixtures ever, with methane as gas component and a specific corn starch as dust sample, the practicality of the whole procedure, the scattering of the results and the deviation between the testing apparatuses is investigated. This paper summarizes the experimental procedure adopted and objectives of the first round-robin phase involving three of the four original German companies, plus volunteering laboratories from Australia, Belgium, Czech Republic, France, Poland and P.R. China. The results will have an impact on the new standard and may lead to robust data for later simulation purposes.
In dem Vortrag werden die Highlights und Ergebnisse des abgeschlossenen Wipano Forschungsprojekts "Spannstahlsicherheit" berichtet. In dem Vorhaben wurde das Projektziel ein neues Prüfverfahren für die Prüfung von Spannstählen auf Spannungsrisskorrosionsempfindlichkeit zu entwickeln erfolgreich abgeschossen. Weiterhin wurden neue Erkenntnisse zu den Ursachen der Ergebnisstreuung der bisherigen Prüfung gemäß ISO 15630-3 gewonnen. Das neue Prüfverfahren soll bei der nächsten Überarbeitungsrunde der ISO 15630-3 als Verfahren zunächst in den informativen Anhang aufgenommen werden.
Polyurethane foams (PUF) are generally flammable, so they are limited in some applications due to strict fire safety requirements. In this study, three distinct industrial benchmark polyurethane foams containing synergistic combinations of expandable graphite (EG) and phosphorous flame retardants (P-FR) were investigated one by one for their fire performance and smoke behavior. This paper aims to substantiate the hypothesis that the combination of EG and P-FR used in polyurethane foams yields a top-notch composite in terms of flame retardancy and smoke behavior by meeting the demanding requirement of low maximum average heat emission (MARHE) and smoke emission in a variety of applications, like advanced materials in construction, lightweight materials for railways, and more.
Leather is considered a luxury good when used in seating and upholstery. To improve safety, flame retardancy in leather is usually achieved through various finishing processes such as spray or roller coating. These treatments require processing steps that cost time and are laborintensive. One avenue to achieving flame retardancy in leather is to add flame retardants during the tanning process. However, the influence on flame retardancy exerted by specific intumescent additives specifically added during leather tanning has yet to be investigated. This work explores the roles played by intumescent additive compounds in flame retarding leather when they are added during tanning instead of applied as a coating. Via a systematic investigation of various compound mixtures, the flame retardant effects in the condensed and the gas phases are elucidated. The results show a strong impact of melamine in the gas phase and of polyphosphates in the condensed phase. Their impact was quantified in fire and smoke analysis, showing a 14% reduction in the peak of heat release rate, strongly reduced burning lengths, and a 20% reduction in total smoke release compared to nontreated leather. These results illuminate the key role played by specific compounds in the flame retardancy of leather, particularly when they are added specifically during the tanning process instead of being applied as a coating.
This method has great potential to reduce processing steps, lower costs, and improve material safety.
Ultrasonic Coda Wave interferometry has the potential to detect minute changes in scattering materials like concrete. By permanently installing ultrasonic transducers in concrete, DFG Research unit CoDA aims to develop methods for concrete damage assessment in Germany's aging infrastructure. To test the methods developed in simulations and laboratory experiments on a large scale, we have implemented several ultrasonic transducers at the Gänstorbrücke Ulm, one of Germany's most monitored road bridges. Since fall 2020 we are monitoring parts of the center of the Bridge, as well as an abutment, and compare the results to the commercial monitoring system. All data is recorded with a self-made data collection device, the so-called W-Box, and analyzed with different coda wave-based algorithms to detect signal and volumetric velocity changes. The long-term measurements show that the influence of temperature changes on strains and therefore ultrasound velocity changes calculated with coda waves can be monitored. The capabilities and limitations of the coda wave-based monitoring system are tested in a controlled experiment. Static loading using a truck with varying loads at several positions allows the calibration of the system to improve the detectability of possibly damaging loads and changes induced by this loading. A map of velocity change analyzing data from this load experiment shows that the influence of load on the material and strain distribution can be detected with array measurements.
Ultrasonic Coda Wave interferometry has the potential to detect minute changes in scattering materials like concrete. By permanently installing ultrasonic transducers in concrete, DFG Research unit CoDA aims to develop methods for concrete damage assessment in Germany's aging infrastructure. To test the methods developed in simulations and laboratory experiments on a large scale, we have implemented several ultrasonic transducers at the Gänstorbrücke Ulm, one of Germany's most monitored road bridges. Since fall 2020 we are monitoring parts of the center of the Bridge, as well as an abutment, and compare the results to the commercial monitoring system. All data is recorded with a self-made data collection device, the so-called W-Box, and analyzed with different coda wave-based algorithms to detect signal and volumetric velocity changes. The long-term measurements show that the influence of temperature changes on strains and therefore ultrasound velocity changes calculated with coda waves can be monitored. The capabilities and limitations of the coda wave-based monitoring system are tested in a controlled experiment. Static loading using a truck with varying loads at several positions allows the calibration of the system to improve the detectability of possibly damaging loads and changes induced by this loading. A map of velocity change analyzing data from this load experiment shows that the influence of load on the material and strain distribution can be detected with array measurements.
This talk provides a brief overview on some geomechanical phenomena and problematic issues in the field of offshore wind-energy geotechnics, with reference to their associated challenges for a numerical analysis/simulation. These may include large deformations, fluid coupling and grain-scale phenomena, all of which are generally difficult to be addressed with conventional FE techniques.
These challenges are illustrated here with a practical example for the retrofit of axially loaded piles using compaction grouting techniques. In this case, the mechanical effects of the retrofit may be analysed with standard FE techniques, but require the adoption of strong assumptions, while the injection process itself can only be analysed with special techniques such as the MPM.
Finally, an LBM-DEM framework for the micromechanical analysis of such problems is introduced and a practical application for the estimation of the soil resistance to driving (SRD) in layered profiles is discussed.
EU project ODYSSEUS - year 1
(2022)
Vorstellung EU-Projekt ODYSSEUS zum Thema Home-Made-Explosives sowie erste Ergebnisse bzgl. Rezepten, Ausgangsstoffen und Home-Made-Explosives in diesem Zusammenhang.
The volumetric energy density of a gas can be increased by liquefaction, which occurs when the gas is cooled below the saturation point. Liquefied gases of great importance to the energy transition are Liquefied Hydrogen (LH2) and Liquefied Natural Gas (LNG), which can be liquefied at temperatures below 160°C. Systems for storing these gases typically must be overpressure resistant and require thermal super insulations (TSI) to hold cryogenic conditions and minimize boil-off losses from evaporation. TSI with vacuum and MLI or perlites are suitable for many applications involving LNG and LH2. Such systems are typically double-walled structures where the inner wall is in contact with the cryogenic liquefied gas. MLI or perlites are located in the gap between the inner and the outer wall, that is kept under vacuum conditions. This combination of insulations strongly reduces the heat transfer between the environment and the cryogenic liquefied gas. From an economic point of view the systems are well sophisticated. However, knowledge of the behavior of this kind of systems in a typical event such as a fire is limited, but necessary to evaluate the safety of the increasing number of applications.
The objective of the research is to determine how TSI behaves at different fire temperatures during fire exposure and afterwards. Special attention is paid to changes in the heat flux, the material properties and vacuum state over time. For this purpose, thermogravimetric analysis (TGA) studies have been carried out. In addition, a test rig was developed that allows testing of TSI at temperatures up to 1000°C under realistic integration conditions and subsequent analysis of the TSI samples. In the test rig the double-wall with vacuum and MLI or perlites inside is simulated. The fire conditions are simulated on one side of the double-wall by adjustable electrical heating elements. This process allows the implementation of repeatable heat flows of up to 100 kW/m². On the other side of the double-wall, cold or cryogenic conditions are simulated with a heat exchanger through which water or the vapor of liquid nitrogen (approx. -196°C) flows. The heat exchanger is also used to determine the heat flux through the double-wall. Thus, the test rig allows thermal loading and performance analysis of TSI samples at the same time.
Compared to tests with real cryogenic systems, tests with this experimental setup have the advantage that, first, the instrumentation is easier to realize, and a higher repeatability is ensured. Second, the local heat flow can be determined over time, and the sample of a TSI can be taken non-destructively and thus analyzed. Third, the tests are less risky as well as time+ and material intensive, so that more tests and variants can be investigated with the same budget.
Preliminary results obtained considering several types of MLI under vacuum show that all observed typs of MLI can be damaged under strong thermal loading. The damages observed were outgassing, melting, shrinkage, cracking, lump formation, and concomitant local loss of the MLI's function as a radiation shield. However, the study also shows that a damage does not always have an extreme effect on the insulating performance.
Earth buildings and adobe construction have been in use for thousands of years. Loam is locally available, environmentally friendly and has a small CO2 footprint mainly resulting from extraction and transport. Because of these reasons loam is one of the building materials of the future.
Water resistance is an important aspect when using loam as a construction material. If the structural option of building protruding roofs cannot be implemented, the water resistance of clay can be improved by stabilization.
Positive properties of the material should not be diminished by stabilization. For example, the desired regulation of air humidity, which however cannot be fully preserved by cement stabilization.
For an alternative and more appropriate stabilisation, different mixtures with calcined clays with alkali activator were examined. The calcination temperature for clays is usually lower than for cement and starts at 600° C. The calcined clays therefore also have a lower CO2 footprint compared to cement. To keep the mixture environmentally friendly potassium was used as alkali ion. It could be proven that the alkali activated polymer enhances water resistance of the loam mixture. Provided some further optimization the material shows potential to replace cement without compromising on the positive properties of clay.
The low calcination temperature for clays (600° C) and a low CO2 footprint compared to cement make them an interesting material. To find a stabilization method for loam using calcined clays, activation by alkalis was necessary. Therefore (and to keep the mixture environmentally friendly) KOH was used as alkali activator. It could be proven that the alkali activated polymer enhances water resistance of the loam mixture.
Der Vortrag stellt die wesentlichen Inhalte sowie die wichtigsten Änderungen der TRGS 510 "Lagerung von Gefahrstoffen in ortsbeweglichen Behältern" vor.
Die TRGS 510 zeichnet sich durch ein gestuftes Maßnahmenkonzept in Abhängigkeit von der Art und Menge der gelagerten Gefahrstoffe aus. Folgende Maßnahmenstufen werden durch die TRGS 510 beschrieben:
1. Kleinmengen -> Allgemeine Maßnahmen
2. Überschreitung der Kleinmengen -> Lagerung im Lager
3. Überschreitung bestimmter Mengen für spezielle Gefahrstoffe -> Spezielle Maßnahmen
4. Verschiedene Gefahrstoffe und Lagerung im Lager erforderlich -> ggf. Getrenntlagerung und Separatlagerung
According to the NBI database, more than 21,000 in-service U.S. bridges lack sufficient structural documentation necessary for analytical load rating. Among these are a significant proportion of older prestressed concrete bridges. Given the lack of documentation on the reinforcing layout, such structures cannot be load rated analytically and are often subject to engineering judgement as the basis for rating. Otherwise, the typical approach for load rating such bridges is to conduct costly proof load testing and destructive probing together with making conservative assumptions. Therefore, any improvement to current practices will benefit DOTs and taxpayers alike. Accurately reconstructed 3D images of the girders to reflect the internal reinforcement could mitigate the need for costly, if not impractical, destructive testing and proof load testing, and help reduce dependency on conservative assumptions. This study examines a comprehensive NDE approach using ultrasonic tomography and GPR to aid in gathering structural information for load rating purposes. Different types of AASHTO and hollow core girders were tested.
Reaktive Brandschutzsysteme finden im baulichen Brandschutz Anwendung zur Erhöhung des Feuerwiderstands von Stahlkonstruktionen. Neben den Anforderungen an die Feuerwiderstandsdauer können damit auch Ansprüche an die Ästhetik erfüllt werden. Die profilfolgende Applikation und die geringen Trockenschichtdicken der Produkte ermöglichen es, das filigrane Erscheinungsbild von Stahlkonstruktionen aufrechtzuerhalten. Neben der thermischen Schutzwirkung muss auch die Dauerhaftigkeit der Brandschutzbeschichtung sichergestellt werden. Die Bewertungsmethoden, die auf europäischer Ebene durch das EAD 350402-00-1106 zur Verfügung stehen, zielen auf eine Nutzungsdauer von zehn Jahren ab. Prüfverfahren für einen darüber hinausgehenden Zeitraum sind nicht beschrieben. In diesem Beitrag werden experimentelle Untersuchungen zum Einfluss der Bewitterung auf das Expansionsverhalten, zur thermischen Schutzwirkung und zu den während des Aufschäumens im Brandfall stattfindenden Reaktionen vorgestellt. Die Versuche wurden an einem wasserbasierten und einem epoxidharzbasierten reaktiven Brandschutzsystem durchgeführt. Die Ergebnisse wurden im Rahmen des IGF-Forschungsvorhabens 20470 N erzielt.